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4th small hole in late model clusters?

Discussion in 'Electrical & Audio' started by Daveo91Burb, Feb 23, 2021.

  1. Daveo91Burb

    Daveo91Burb Full Access Member

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    Was it ever used for anything in the late model squares? Or was it always blanked? The reason I ask is I have my cluster all taken apart right now and I noticed there are three holes for the typical light socket used for gauge lighting, turn signals, idiot lights, etc. And my cluster was modded by the PO for a trans temp gauge there, so I can't tell for certain, but it looks like there were dividers there so that hole could have been used for three separate idiot lights. I traced the paths on the printed circuit back to the main connector and two of the three don't even have pins, but one does - looks like it goes to a brown wire.

    Any thoughts?

    I will take a pic tomorrow and post if it helps. I should have done it when I was out in the shop tonight.
     
  2. PrairieDrifter

    PrairieDrifter Full Access Member

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    Many variations, depending on trim level, and what people ordered. This is an 84 and a 79, the 84 is just a blank spot, but it's only covered by the black piece that overlays. The 79 is a clock

    E1620DA6-C5AC-4F17-B39F-CC1A23BA7B00.jpeg

    1FA92E0A-2B3A-4AC6-8B49-1BF645596387.jpeg
     
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  3. ali_c20

    ali_c20 Full Access Member

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    This is a 78 gauge cluster with tach.

    78tach01.jpg

    Cluster w/o tach contains idiot light
    clusternontach.jpg
     
    Last edited: Feb 23, 2021
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  4. CorvairGeek

    CorvairGeek Full Access Member

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    Someone posted a pic of a later one with a volt (battery) symbol in one, there may have been others in the hole too. I believe it was an the electronic speedo version.
    Not sure what it would take to search for it.
     
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  5. gmbellew

    gmbellew Full Access Member

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    my 1990 (electronic speedo) has an alternator charging dummy light in that spot.
     
  6. Turbo4whl

    Turbo4whl Supporting Member Supporting Member

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    Medium duty squares have a tachometer with a fuel gauge in the bottom. There would be a brake air gauge in the fourth small hole.

    I installed this type tach in my '82 and put the turbo boost gauge in the fourth hole. In this picture you can see the tach with fuel gauge:

    IMG_3344.jpg

    If anyone is lucky enough to find this tachometer, you need to remove the fuel gauge resister from the back of your original fuel gauge and use it to replace the resister on the medium duty tach/ fuel gauge. Then the fuel gauge will be correct.
     
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  7. Craig Nedrow

    Craig Nedrow Full Access Member

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    Modded for a 2 1/8 auto meter tac, and an AEM AF ratio gauge, both helpful tuning aids.

    IMG_3576~photo.JPG

    IMG_3063~photo.JPG
     
  8. Craig Nedrow

    Craig Nedrow Full Access Member

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    Want to replace the worthless amp gage with a voltmeter gauge. My 85 has a volt meter, much better. Need to get a better setup for the wipers, the one in the pic swipes three times and parks. Fortunately we don't get much rain...
     
  9. Daveo91Burb

    Daveo91Burb Full Access Member

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    Here's what I'm talking about.

    IMG_1725.jpeg IMG_1728.jpeg

    There are three light socket holes and originally there were dividers between them - looks like provisions for three separate idiot lights in that hole? But I've never seen anything like that in the 4th hole - on any year square?

    My questions are specific to the late models. i.e. tach option went away in early 80s (?) so there wouldn't be a fuel gauge there, and the radios all went electronic in '89 (?) so after that they would have never put a clock there.

    Second pic shows the main cluster connector. Two of those three light socket holes trace to the two empty slots (6 and 7) by my thumb. But the third one traces to slot 5, with a brown wire going somewhere. My question boils down to what's that brown wire leading to? Do the wiring diagrams show the pin outs for the instrument cluster?
     
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  10. Daveo91Burb

    Daveo91Burb Full Access Member

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    I'm one of the lucky ones to have the aftermarket version of this tach that was produced by GM Sports - lucky because I believe it went out of production a few years ago. Love having the fuel gauge in with the tach. PO put a B&M trans temp gauge in the 4th hole - I didn't want to have to take that out for a fuel gauge.

    I have that same AEM A/F gauge, but I have an A/C vent where you put yours. Fortunately the gauge fits perfectly in the ashtray - and I don't smoke. I can close the ash tray if I don't want to see A/F.
     
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  11. Daveo91Burb

    Daveo91Burb Full Access Member

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  12. bucket

    bucket Super Moderator Staff Member

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    In the late 80's and early 90's, GM had a habit of including extra idiot lights that may or may not have ever been put to use. Often with markings in the cluster face too. Or sometimes they actually did get used, but it was for an obscure option that nobody really ever saw.

    Perhaps the one that is actually wired in was for a daytime running lamp indicator for Canadian models?
     
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  13. Turbo4whl

    Turbo4whl Supporting Member Supporting Member

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    @Daveo91Burb

    [​IMG]


    Very cool! And that tach 0-7000 instead of 0-5000 like the truck tach. I did see that tach on GM Sports, but is was already listed as not available.
     
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  14. Daveo91Burb

    Daveo91Burb Full Access Member

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    Yeah, I think they've been out of production for a couple years. I did a little research last night - sounds like the guy that made them died unexpectedly. :-( Even if I did sell my burb (highly unlikely) I think I'd keep that tach!
     
  15. Daveo91Burb

    Daveo91Burb Full Access Member

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    Sounds like as good a theory as any I've come up with! I'm mostly just curious. I may try and put a another cluster light (that comes on with headlights) in one of those holes - The AutoMeter trans gauge has a dedicated light but it's so much brighter than the other gauges. If I left the bulb out and had a light in one of those holes I think it would shine through enough to illuminate the gauge.
     

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